alwang wrote:
Thanks! The optical quality would seem to be a balancing act. On the negative side, you have the optical aberrations of the adapter. On the positive side, the aberrations of the lens itself are compressed in the image. Then on the negative side again, you're using more of the periphery of the lens' image circle, which is likely lower IQ than the center. It'll be interesting to see how all this balances out in practice.

You will of course not win anything compared to using the same lens on FF, except if the APS-C sensor is more modern technology. But until there is a small FF camera with interchangable lenses, this is a very nice product if it works alright.
The exit pupil will of course get closer to the sensor, so whatch out for corner smearing because of the microlens array and stuff like that. I suppose it will work reasonably equal to M lenses in that respect.